The present invention relates to a high reliability fiber coupled switch. In particular, the present invention relates to a fused coupler optical switch (FCOS) that functions as a bidirectional optical cross-bar switch. The switch uses a magnetic field to bend the coupled region to switch between cross and bar states. The strain resulting from such bending causes the coupled fibers to lie along different bend radii resulting in a variable power coupling ratio.
Fiber optic communication systems now use optical fiber cables to transmit information within communications networks such as wide area networks and local area networks. Switches permit optical paths within the network to be changed to allow for the information to be directed to a particular unit or units or even to bypass a particular unit. Switches for such uses must exhibit a high degree of reliability over many switch cycles, low insertion loss, low crosstalk, and short switch times.
Several forms of optical fiber switches are known. In some switch arrangements the switching function is accomplished by placing an optical device within the optical path. One type of prior art optical switch utilizes a movable blocking element to switch light from one fiber to another or to an off position. U.S. Pat. No. 4,790,621 (Calaby et al.) discloses the use of a movable prism to switch light from one fiber to another. U.S. Pat. No. 4,261,638 (Wagner) discloses the use of a reflecting member to switch light along different optical paths.
Mechanical switching arrangements are also known. In such devices an optical fiber is fixedly mounted to a movable member and the member is physically displaced from a first to a second position to switch the optical path. U.S. Pat. No. 4,911,520 (Lee) utilizes a cantilevered glass tongue to which a fiber is edgewise mounted. A first and a second fiber are similarly mounted along the edges of a fixed block. Moving the glass member from a first to a second position removes the fiber thereon from a first optical path that includes the first fixed fiber and places the fiber into a second optical path that includes the other fixed fiber.
In U.S. Pat. No. 4,407,562 (Young) optical fibers are secured in grooves disposed on the exterior surface of a movable housing. Displacement of the housing brings the faces of the fibers into and out of alignment with other arrays of fibers, thereby to cause the switching action. Alignment of the movable housing with the casing in which it is disposed is effected using alignment grooves. U.S. Pat. No. 4,896,937 (Kraetsch et al.) provides two V-grooves, one in the cover and another in the base of the housing. The switching action is accomplished by moving a ferromagnetic strip to which a fiber is attached into position in one of the V-grooves.
U.S. Pat. No. 4,759,597 (Lemonde) mounts an optical fiber to a magnetic rocker arm. The pivotal motion of the rocker arm moves the fiber between corresponding fibers secured in grooves respectively provided in an upper and a lower support slab.
U.S. Pat. No. 4,946,236 (Dautartus et al.) discloses a switch in which the displacing force is applied to the fiber itself. The switch includes fibers that are surrounded by a magnetic sleeve. The fibers are disposed within grooves defined by the corners of an elongated, diamond shaped, internal channel extending through a block. A magnetic field is applied to effect the displacement of the fibers from one corner of the groove to another.
U.S. Pat. No. 5,175,776 discloses an optical fiber switch comprising a base having a block portion thereon. The block has a surface in which at least a first and a second groove are formed. An optical fiber has a first predetermined portion of its length adjacent to its end face received in one of the grooves. The axis of the fiber in this first predetermined portion of the fiber spaced behind the first portion is mounted over an inclined ramp, thereby bending the portion of the fiber forwardly thereof. The biasing force is generated by the bending of the fiber. Preferably, the surface of the ramp defines an angle with respect to the base that lies in a range from five (5) to fifteen (15) degrees. The ramp may be grooved, if desired. A switching member is reciprocally movable with respect to the base from a first to a second position. The motion of the switching member is generally transverse to the direction of the biasing force. During its movement, the switching member engages operatively against the fiber thereby to move the first predetermined portion thereof against the biasing force out of the one groove and into the other groove. As the fiber is displaced, the biasing force acts thereupon to urge the first predetermined portion of the fiber toward the bottom of that other groove. In the preferred instance the switching member takes the form of a yoke connected via a rocker arrangement to an actuating solenoid. The yoke engages operatively against an intermediate portion of the fiber disposed between the ramp and grooved block.
The above described prior art optical switches suffer from a number of shortcomings with respect to packaging, including fiber bend radius and environmental sensitivity, performance and reliability, and manufacturability.
In another prior art reference, U.S. Pat. No. 5,146,519 to Miller et al. (and assigned to the assignee in this application), discloses a fiber coupler optical switch that operates by rotating the coupler at one end between bent and coupled states, such that the coupling characteristics are tunable based on the degree of rotation.
In view of the foregoing, it is an object of the present invention to provide an optical switch which has a relatively large (low stress) fiber bend radius, is relatively insensitive to changes in environmental conditions such as temperature, has a highly reliable performance, is easily and repeatably manufacturable, and can adjust the coupling characteristics based on linear displacement.
In accordance with an illustrative embodiment of the invention, an optical switch includes fused coupler, preferably formed of glass, has first and second ends and a coupling region therebetween. There are first and fourth optical ports at the first end of the coupler and second and third optical ports at the second end of the coupler. A clamping element fixedly clamps the first end of the coupler in an elastomeric support for the reduction of concentrated stress in the coupler element. The second end of the coupler is free. A magnetic sleeve surrounds the coupler near the free end. A first stop block is located on one side of the sleeve. A second stop block is located on the opposite side of the sleeve from the first stop block. There is a circuit for generating a first magnetic field which causes the sleeve to move into contact with the first stop block and for generating a second magnetic field which causes the sleeve to move into contact with the second stop block. In the first position (contact of the coupler with the first stop block), the first port is optically connected with the second port and the fourth port is optically connected with the third port. In the second position (contact of the coupler with the second stop block), the first port is optically connected with the third port and the fourth port is optically connected with the second port.
In a preferred embodiment of the invention, the first stop block comprises a first flat stop and a first V-groove stop. Similarly, the second stop block may comprise a second flat stop and a second V-groove stop. The inventive optical switch may include a sensor element such as a Hall element for detecting the first magnetic field or the second magnetic field, thereby detecting the state of the optical switch.
In another preferred embodiment, there is an athermalized joint between the sleeve and the coupler. The athermalized joint is formed from an elastomeric material for matching coefficients of thermal expansion of the coupler and the sleeve. Note that the locations of the attachments between the stop blocks and the substrate base are chosen for purpose of athermalization and are subject to the materials used.